So this is probly a qustion that is weird but how do you know that a stud is gonna be a good one for better foals without just spam breeding to them?

From my view, you never know if they'll be good or not. You never know with any horse. Then might be good producers if they're sent to strong mares, but they may not. They might be horrible producers with testing mares, but they could be. Tracking the training of stallions, mares too, can help determine if they possibly could, but still a 50/50. You just have to hug RF and give it a limb, then hope for the best.